A number of various means and procedures have been developed in recent years to remove obstructions to clear or open occluded arteries in order to restore the necessary circulation through the body. One approach is the so-called coronary "bypass" operation which requires a large incision into the body to open the chest cavity. This procedure is fairly traumatic to the body, and is quite drastic. Thus, other approaches for removing obstructions have been developed.
One alternate approach is the use of well known angioplasty procedures. A catheter is inserted through a small incision into the body through an artery to the site of the obstruction. The catheter incorporates a balloon to open the vessel by flattening the obstructive tissue against the vessel wall. With the angioplasty procedures, however, the obstructive tissue causing the occlusion remains in situ after the procedure is performed. Thus, while the problem may be alleviated, it is not eliminated. Also, there remains the real probability there will be a restenosis.
Another approach is the use of atherectomy procedures in which a catheter inserted into the artery includes a cutter head. Obstructive tissue causing the occlusion in the vessel is excised by the cutter from the lumen of the vessel. As should be readily apparent, the instruments used for this procedure incorporate precisely designed miniature cutting devices. Further, the devices require special fabrication and design considerations to allow satisfactory operation within the lumen of a vessel. Specifically, both the cutting device itself and its attendant drive elements which are inserted into the vessel with the cutting device must be miniaturized.
Several atherectomy related devices have been previously disclosed. Exemplary of such devices is U.S. Pat. No. 4,754,755 to Husted which discloses a catheter with a cylindrical rotary blade that is used to clear arterial obstructions. Another device is that disclosed in U.S. Pat. No. 4,273,128 to Lary for a coronary cutting and dilating instrument. It includes a balloon in combination with radially extending knife blades to permit incision and immediate dilation of the artery.
For each of the devices disclosed in these references, however, the effective cutting area of the blade of the device is limited. This is so because, in these conventional devices, the cutting action of the rotating blade does not extend beyond the periphery of the tubular structure or sheath which is used to feed the rotating blade through the artery or vessel. Consequently, the effective cutting capability of the blade inside a vessel is limited to a diameter which is equal to or less than the diameter of the blade. A diameter of cutting action which is greater than that of the blade is desired, however, to allow the cutter and its attendant sheaths or catheters to advance properly through the obstructive tissue, and to prevent the device from getting stuck in the vessel. Further, it is desirable that the cutting device not occlude fluid flow through the vessel, either when it is operational or when it is inoperative. Fluid should be able to flow around and past the cutting device at all times. Thus, there is a need for a cutter which has the capacity for cutting extended diameters. Accordingly, the present invention recognizes the need for an atherectomy cutter whose effective cutting action diameter extends beyond its base and attendant basic diameters to increase the cutting effectiveness of the device.
It is thus an object of the present invention to provide a cutter for an atherectomy device which has expanded cutting action when it is rotated inside the lumen of a body vessel. Another object of the present invention is to provide an atherectomy device which can be operatively positioned within the lumen as required to excise obstructive tissue from inside the lumen of a body vessel. Yet another object of the present invention is to provide a cutting device which allows fluid flow through the vessel around and past the cutting device. Still another object of the present invention is to provide an atherectomy device which can be effectively advanced during the cutting of obstructive tissue from the inside of a body vessel. Yet another object of the present invention is to provide an atherectomy device which is cost effective in its relative ease of use and manufacture.